Create feature flag for Zebra#9 design update

- Create a feature flag that will enable/disable the upcoming zebra design
- This feature flag will add a class on the `body` html element that will enable & disable the new design.
- class names:
 -- enabled: vector-feature-vector-zebra-design-enabled
 -- disabled: vector-feature-vector-zebra-design-disabled

Bug: T332448
Change-Id: I264f2a338130e95543c20b592addf954a119b56a

includes/Constants.php

@@ -280,6 +280,21 @@ final class Constants {
 	 */
 	public const CONFIG_DEFAULT_LIMITED_WIDTH = 1;
 
+	/**
+	 * @var string
+	 */
+	public const FEATURE_ZEBRA_DESIGN = 'ZebraDesign';
+
+	/**
+	 * @var string
+	 */
+	public const REQUIREMENT_ZEBRA_DESIGN = 'ZebraDesign';
+
+	/**
+	 * @var string
+	 */
+	public const CONFIG_ZEBRA_DESIGN = 'VectorZebraDesign';
+
 	/**
 	 * This class is for namespacing constants only. Forbid construction.
 	 * @throws FatalError

includes/ServiceWiring.php

@@ -295,6 +295,26 @@ return [
 			]
 		);
 
+		// Feature: T332448: feature Zebra#9 design update
+		// ================================
+		$featureManager->registerRequirement(
+			new OverridableConfigRequirement(
+				$services->getMainConfig(),
+				$context->getUser(),
+				$context->getRequest(),
+				null,
+				Constants::CONFIG_ZEBRA_DESIGN,
+				Constants::REQUIREMENT_ZEBRA_DESIGN
+			)
+		);
+		$featureManager->registerFeature(
+			Constants::FEATURE_ZEBRA_DESIGN,
+			[
+				Constants::REQUIREMENT_FULLY_INITIALISED,
+				Constants::REQUIREMENT_ZEBRA_DESIGN,
+			]
+		);
+
 		return $featureManager;
 	}
 ];

skin.json

@@ -623,6 +623,10 @@
 				"logged_out": true
 			},
 			"description": "@var array Moves the tools links from the main menu into a new menu in the page toolbar"
+		},
+		"VectorZebraDesign": {
+			"value": false,
+			"description": "@var boolean Temporary feature flag that enables the zebra design for the Vector skin."
 		}
 	},
 	"ServiceWiringFiles": [